The invention relates to a method for supporting and hydrodynamically centering a rotating workpiece during machining on a workpiece machine/grinding machine, and relates to a steady for performing said method.
Usually centering steadies are used for supporting rotating workpieces during grinding. This support is necessary in order to prevent the workpiece from sagging from the effect of the forces of the grinding wheel that are acting in the transverse direction. For this, support bodies are used that contact the workpiece at a plurality of locations and center it with respect to the axis of rotation. The support is generally provided in a self-centering manner by means of three support elements arranged on the circumference of the bearing to be supported. Such steadies are known, for example, from DE-OS 1 577 369.
The support elements for such steadies are normally coated with CBN (cubic centered boron nitride) or PCD (polycrystalline diamond) at the contact points, to reduce wear and visible running tracks. Since the steadies contact the workpiece at the support elements, a so-called running track necessarily occurs at the support point. The running track is based on a smoothing of the surface roughness at points of contact and is optically visible. This change in the surface quality can potentially have an unfavorable influence on the lubricating film in the bearing. In addition, the supporting portion changes in this area of the bearing. Although any change in the dimensions of the bearing point in the area of the running track is frequently only minor, such a change is frequently no longer acceptable given constantly increasing technical demands on the bearing points. The finish grinding of the bearing point that is therefore necessary after using the steady leads to an undesired increase in grinding time and thus in unit costs.
Moreover, a steady that supports the bearing at three locations suffers from the disadvantage that a short-wave non-circularity that has occurred on the bearing point during machining is also formed on the bearing point and in at least some cases cannot be compensated. These two effects cannot be entirely prevented with the known steadies.
Another variant of steadies are so-called hydrostatic steadies, such as are described in DE-OS 1 627 998 and EP 1 298 335 B1 (German translation: DE 602 10 187 T2). With these steadies, the bearing point is supported by a hydrostatic bearing in which a plurality of hydrostatic pockets distributed around the interior circumference of the bearing are actuated using a fluid that is under pressure. This produces a hydrostatic pressure on the bearing point of the shaft, and this pressure supports and centers the shaft. The fluid pressure is adjusted using a regulating device. A particular disadvantage of this type of steady is that the bearing point cannot be machined while being supported because it is entirely surrounded by the steady. This variant also requires a special design for the support shell, with support pockets and relief grooves, which leads to complex and expensive production.
According to DE 102 32 394 B4 from Erwin Junker Maschinenfabrik GmbH (Applicant), for supporting a rotating workpiece, at least one cushioned body that can be actuated using a pressure fluid is positioned against the workpiece from the side disposed opposite the grinding wheel.
The positioning force can be influenced pneumatically or hydraulically. In certain embodiments a fluid can be added between the cushioned body and the workpiece as a pressure means and lubricant. One disadvantage of this type of support is the single-sided support of the workpiece and the complex design.
The underlying object of the invention is to provide a method for supporting a rotating workpiece during machining, which method avoids the disadvantages of the prior art, and to propose a cost-effective steady that is suitable for performing the method.